1. Field of the Invention
The present invention relates to a flow control apparatus for heavy construction equipment, which can uniformly supply hydraulic fluid to an actuator, without deteriorating the performance of a hydraulic control valve, in the case where the hydraulic fluid is kept at high temperature and a working device operates on high-load working conditions.
More particularly, the present invention relates to a flow control apparatus for heavy construction equipment, which can prevent overspeed and abrupt operations of an actuator due to an excessive flow rate that exceeds a predetermined flow rate during an initial operation of the actuator when a composite work is performed by simultaneously operating an option device and another actuator, and can prevent the cut-off of hydraulic fluid supply to the option device due to an operation inability of a flow control valve when leakage of the hydraulic fluid occurs due to the increase of the temperature of the hydraulic fluid to a high temperature (that exceeds 90° C.).
2. Description of the Prior Art
As illustrated in FIG. 1, a conventional flow control apparatus for heavy construction equipment includes a hydraulic pump 1; an actuator 13 for option devices connected to the hydraulic pump 1; a variable control spool 12 installed to be shifted by pilot signal pressure in a flow path between the hydraulic pump 1 and the actuator 13; a switching valve 4 installed to be shifted by a difference between pressure in an inlet-side path 5 and pressure in an outlet-side path 6 of the variable control spool 12; and a logic poppet 10 installed to open/close a high-pressure path 2 of the hydraulic pump 1 by a difference between pressure in the high-pressure path 2 and pressure passing through the switching valve 4.
If the variable control spool 12 is shifted by the supply of the pilot signal pressure, the pressure of the inlet-side path 5 becomes relatively higher than that of the outlet-side path 6, and thus the spool of the switching valve 4 is shifted in a right direction as shown in the drawing.
Accordingly, the high-pressure hydraulic fluid fed from the hydraulic pump 1 is supplied to an inlet of a piston orifice 8 via a path 3, the switching valve 4, and a path 7 in order. The hydraulic fluid passing through the piston orifice forms pressure in a back chamber 9, and then is supplied to the inlet-side path 5 of the variable control spool 12 via a poppet path 11 of the logic poppet 10 and an outlet path 3a of the logic poppet in order.
In this case, the pressure of the hydraulic fluid fed from the hydraulic pump 1 to the inlet side of the logic poppet 10 via the path 2 is relatively higher than the pressure of the hydraulic fluid fed from the hydraulic pump 1 to the back chamber 9 in which a loss of pressure has occurred via the path 3, the switching valve 4, the path 7, and the piston orifice 8 in order.
Accordingly, the logic poppet 10 is moved in a downward direction as much as a difference between the pressure fed to the inlet side of the logic poppet 10 through the high-pressure path 2 and the pressure fed to the back chamber 9. Thus, the hydraulic fluid fed from the hydraulic pump 1 is supplied to the inlet side of the variable control spool 12 via the path 2, the logic poppet 10, and the outlet path 3a of the logic poppet in order.
In this case, a valve spring 18 of the switching valve 4 is set to a predetermined pressure (e.g. 20 kg/cm2), and thus the difference between the pressure of the hydraulic pump side and the pressure of the actuator side can be kept in a predetermined pressure range even if the pressure of the hydraulic pump 1 or the actuator 13 is changed. That is, the flow rate being supplied to the actuator 13 can be controlled by determining the amount of movement of the logic poppet 10, so that the flow rate corresponding to the pressure difference can be supplied.
Accordingly, the logic poppet 10 serves as a flow control valve which uniformly increases the flow rate in accordance with the increment of a sectional area, which corresponds to the movement of the variable control spool 12, on condition of a specified set pressure of the switching valve 4.
On the other hand, in the conventional flow control apparatus for heavy construction equipment as illustrated in FIG. 1, no orifice is provided in the poppet path 11 of the logic poppet 10, and if the logic poppet 10 is opened, damping is not performed to cause the logic poppet 10 to be opened abruptly.
As illustrated in FIG. 4, which is a graph showing a change of pressure in the case where an option device and another actuator are simultaneously operated, if the pilot pressure 23 for option devices is changed in a state that the pressure 21 of the hydraulic fluid fed from the hydraulic pump 1 forms the pressure 22 of the actuator, a peak flow rate 24 of the option device side is simultaneously generated, and then the flow rate is stabilized as a controlled flow rate.
That is, as an excessive flow rate that exceeds a predetermined flow rate is fed during an initial operation of the actuator 13, an abrupt operation of the actuator 13 occurs, and the flow rate fed to another actuator is relatively reduced, resulting in that the flow rate fed to the actuator cannot be stably controlled.
As illustrated in FIG. 2, another conventional flow control apparatus for heavy construction equipment includes a hydraulic pump 1; an actuator 13 for option devices connected to the hydraulic pump 1; a variable control spool 12 installed to be shifted by pilot signal pressure in a flow path between the hydraulic pump 1 and the actuator 13; a switching valve 4 installed to be shifted by a difference between pressure in an inlet-side path 5 and pressure in an outlet-side path 6 of the variable control spool 12; a logic poppet 10 installed to open/close a high-pressure path 2 of the hydraulic pump 1 by a difference between pressure in the high-pressure path 2 and pressure passing through the switching valve 4; a poppet orifice 15 installed in a poppet path 11 to suppress the generation of a peak flow rate during an initial operation of the actuator 13; and a check valve 14 for allowing hydraulic fluid to move from an inlet-side path 5 of the variable control spool 12 to a back chamber 9 (i.e. in one direction).
The construction of this conventional flow control apparatus, except for the damping poppet orifice 15 installed in the poppet path 11 and the check valve 14, is substantially the same as that as illustrated in FIG. 1, thus the detailed description thereof will be omitted. The same drawing reference numerals are used for the same elements across various figures.
As the generation of the peak flow rate is suppressed by the poppet orifice 15 installed in the poppet path 11 during the initial operation of the actuator 13, the overspeed and abrupt operation of the actuator 13 can be prevented.
Also, after the flow rate being fed to the actuator 13 is controlled by the logic poppet 10, a re-seat function of the logic poppet 10 can be improved by the check valve 14 installed inside the logic poppet 10 when the variable control spool 12 is returned.
In the flow control apparatus for heavy construction equipment as illustrated in FIG. 2, if the temperature of the hydraulic fluid is increased above a high temperature (e.g. above 90° C.) due to a long-time use of heavy construction equipment such as an excavator, an excessive leakage of hydraulic fluid occurs due to deterioration of the viscosity of the hydraulic fluid.
That is, due to a difference between the pressure in the high-pressure path 2 and the pressure in the back chamber 9 of the logic poppet 10 that keeps a pressure relatively lower than that of the high-pressure path 2, leakage of the hydraulic fluid occurs through a ring-shaped gap formed on a sliding surface of the logic poppet 10.
In the case of one conventional flow control apparatus of FIG. 1, no poppet orifice is installed, and thus the pressure in the back chamber 9 is easily lowered because of the leakage bypassing through the poppet path 11 even if the leakage of the hydraulic fluid occurs. However, in the case of another conventional flow control apparatus of FIG. 2, the pressure in the back chamber 9 is increased by the poppet orifice 15 installed in the poppet path 11 when the leakage of the hydraulic fluid occurs due to the high temperature of the hydraulic fluid, and thus the logic poppet 10 is seated (in upward direction as shown in the drawing) and do not operate any more.
Accordingly, the supply of the hydraulic fluid from the hydraulic pump 1 to the actuator 13 for option devices is intercepted. That is, in the case where the temperature of the hydraulic fluid is low, the actuator is operated, while in the case where the temperature of the hydraulic fluid is high, the logic poppet 10 is seated due to the increase of the pressure in the back chamber that is caused by the excessive leakage of the hydraulic fluid, and thus the actuator is stopped with the supply of the hydraulic fluid intercepted, thereby lowering the working efficiency of the equipment.
As illustrated in FIG. 5, which is a graph showing a change of pressure in the case where an option device and another actuator are simultaneously operated, if the pilot pressure 23 for option devices is changed in a state that the pressure 21 of the hydraulic fluid fed from the hydraulic pump 1 forms the pressure 22 of the actuator, deterioration of the flow rate 25 of the option device side is simultaneously generated, and then no flow rate is fed to the actuator 13 to cause the operation of the option device to be impossible.
Accordingly, the work is not smoothly performed, and thus the working efficiency is lowered.